Why are the number of cores in a processor normally even

Question

Whenever i look at specifications of the processor , the number of cores is always 2 , 4 ,8 .

Is there any reasons why the number of cores are always even and not odd like 3 , 5 , 7

Solution 1

@Tero is correct. The primary reason is because most cores are rectangular. Creating a multi-core processor is done by mirroring a core layout. Mirror rather than stepping to keep like resources on adjacent cores together. During testing a defect may prohibit a core from performing to spec. In that case the core may be disabled and the product sold with n-1 cores. Some products may have an odd number of cores because room is needed for other features like ram or regulators. The core layout for GPU's for example may use a lot of mirrored cores but be laid out very 'unnaturally' to make room for ram or bus interfaces.

Solution 2

I think the main reason for this is the physical layout of the cores on the processor chip. Having an odd number of cores would leave an unused physical slot in the chip.

Solution 3

First, we only had one core. So someone, at some point just decided to double it and make a 2 core system.

Going from there, it's easier to build a 4 core system, because you're just doubling the 2 core system and you already know how to double. You don't need to invent a way for your system to work with 3 cores.

Comments

[DasKrümelmonster]

There are (or have been) AMD triple-core CPUs. These are quad-cores, where testing determined that one is defective. This core is then disabled and the CPU is sold as triple-core.

[Ramhound]

@pbies - Both 12 and 6 are even though. Its really as simply as nobody would purchase a 3 core CPU. Its market driven.

[mpez0]

Actually there are an awful lot of processors with 1 core. Last I checked, 1 was an odd number.

[DasKrümelmonster]

Looking at the die shot of a Haswell CPU, I would not expect such unused physical slot. The chip could shink a little bit horizontally and have little less L3 cache.

[Sun]

Makes you wonder why manufacturers just don't disable the one and sell you the next even down but give you 7-core. I remember buyers specific wanted certain models/runs of CPUs because they read certain ones could be overclocked more reliably. Same sort of thing with something sold as 6-core, but might have a reputation of being able to add one more core reliably for certain models/runs. Kind of an advanced hobbyist peformance secret.

[CrazyCasta]

@sunk818 I don't think you understand my answer. They are so integrated that it may well be impossible to disable one without the other.

[Kraken]

What if intel made a quad-core cpu and one of those cores was buggy? Would they blow 2 cores instead of one?

[John Yost]

If they can sell the product with 2 cores didabled and still make a profit then yes, absolutely. Why waste silicon if they can still sell it.

[Kraken]

Why can't they just sell it for a better price by labeling it as a 3 core processor. Like, I believe, AMD once did with Athlon II X3.